pasting
using System.Linq; using System.Text.RegularExpressions; using System.Windows; using System.Windows.Controls; using System.Windows.Input; namespace OnlyCapsNumbers { public partial class MainWindow : Window { // ✅ Allowed chars: A–Z and digits private static readonly Regex AllowedRegex = new Regex("^[A-Z0-9]$"); public MainWindow() { InitializeComponent(); } // Block invalid typing private void txtInput_PreviewTextInput(object sender, TextCompositionEventArgs e) { e.Handled = !AllowedRegex.IsMatch(e.Text); } // Sanitize pasted text (check each character) private void txtInpu...